A blind nut includes an internal threading portion, a tube-shaped portion continuing from the internal threading portion, and a flange at the end of the tube-shaped portion. A blind nut is inserted into a hole in a mounted member and a fastening tool is used to cause the tube-shaped portion to buckle, expanding the diameter of the tube-shaped portion, interposing the mounted member between the buckled tube-shaped portion and the flange, and securing the blind nut to the mounted member. The external threading of a bolt can then be screwed into the internal threading portion of the blind nut to secure another mounted member. Because a blind nut can be used from one side of a mounted member, it can be used to fasten a nut to a mounted member such as a panel whose opposite side can be difficult to reach.
FIG. 1 is a front view, including a partially cut away cross-sectional view, showing a blind nut 10 of the prior art. The blind nut 10 is cylindrical and is axially symmetrical the entire length along a central axis. An internal threading portion 11 is provided at one end. The internal threading portion 11 is cylindrical, and internal threading 15 is formed inside. The external threading of a fastening tool can be screwed into the internal threading 15. The tube-shaped portion 13 continuing from the internal threading portion 11 is cylindrical, and is thinner than the internal threading portion 11. This portion buckles when the blind nut is mounted on a mounted member 41. The blind nut 10 has a flange 14 at the end opposite the internal threading portion 11. The outer diameter of the flange 14 is greater than the inner diameter of the mounting hole 43 in the mounted member 41 so that, when the blind nut 10 is inserted into the mounting hole 43 in the mounted member 41, the bottom surface of the flange 14 comes into contact with the upper surface of the mounted member 41 and stops. A through-hole 16 is formed from the side end portion of the flange 14 to the internal threading portion 16. The inner diameter of the through-hole 16 is constant from the side end portion of the flange 14 to the tube-shaped portion 13, and the inner diameter becomes smaller in the internal threading portion 11.
FIG. 2 is a front view, including a partially cut away cross-sectional view, showing the blind nut 10 mounted in the mounting hole 43 of a mounted member 41. When the blind nut 10 is mounted using a fastening tool, the thin tube-shaped portion 13 buckles to become an enlarged-diameter portion 17, the mounted member 41 is interposed between the enlarged-diameter portion 17 and the flange 14, and the blind nut 10 is mounted in the mounted member 41.
The length of the tube-shaped portion 13 is often changed so that a single type of blind nut can be mounted in mounted members with a wide range of thicknesses. When the length of the tube-shaped portion 13 is too long relative to the thickness of the mounted member 41 and the blind nut 10 is mounted, the thin tube-shaped member 13 does not buckle uniformly to become an enlarged-diameter portion 17 with a uniform diameter around the entire circumference. A section of the enlarged-diameter portion 17 buckles inwardly, the enlarged-diameter portion 17 does not come into contact with the mounted member, and an abnormally deformed portion is likely to be formed which rises up from the surface of the mounted member.
In order to mount a blind nut in mounted members of different thicknesses without abnormally deformed portions being formed, many different types of blind nut have to be prepared with tube-shaped portions of varying lengths. Thus, a single type of blind nut that can be easily mounted in mounted members with a wide range of thicknesses, such as panels, is desired.
A blind nut is disclosed in Patent Document 1 which has an internal threading portion, a hollow tube-shaped portion, and a flange. This thick blind nut, which has a wide outer diameter, is inserted into a hole in a panel, and the tube-shaped portion is buckled to fix the blind nut in the panel using the buckled tube-shaped portion and the flange. The outer diameter of the tube-shaped portion becomes gradually smaller towards the internal threading portion. The blind nut in Patent Document 1 is problem-free because the position in the tube-shaped portion where the buckling begins is determined beforehand. The position where the blind nut begins to become deformed is the position corresponding to the surface of the mounted member or a position in the tube-shaped portion adjacent to the internal threading portion. However, the blind nut in Patent Document 1 cannot be fastened to mounted members with a wide range of thicknesses.
A blind nut is disclosed in Patent Document 2 which as an internal threading portion, a hollow tube-shaped portion, and a flange. This blind nut is inserted into a hole in a panel, and the tube-shaped portion is buckled to fix the blind nut in the panel using the buckled tube-shaped portion and the flange. In this blind nut, the tube-shaped portion has a cylindrical portion that is thinner than the internal threading portion, and a compressed-diameter portion formed between the cylindrical portion and the internal threading portion. When this blind nut is fastened, the tube-shaped portion begins to bend at the compressed-diameter portion. However, the length of the compressed-diameter portion is short, so the blind nut in Patent Document 2 cannot be fastened to mounted members with a wide range of thicknesses.
Therefore, a single type of blind nut is desired that can be easily mounted in mounted members such as panels having a wide range of thicknesses. Also desired is a blind nut having a tube-shaped portion whose diameter can be sufficiently enlarged to ensure reliable mounting in a mounted member.